Merge #13543: depends: Add RISC-V support

974f0bf8e6 depends: Mention RISC-V known compilation issue with gcc-7.3.x (Wladimir J. van der Laan)
0d1f38c45f depends: update zmq config.guess/config.sub for riscv support (fanquake)
409481c465 depends: latest config.sub (fanquake)
d7005e9988 depends: latest config.guess (fanquake)
359e2e3525 depends: Add RISC-V support (Wladimir J. van der Laan)

Pull request description:

  This adds support for riscv32 and riscv64 builds to the depends system.

  The change consists of documentation and build system changes. The most significant change is an update of `config.sub` and `config.guess` inside zeromq patch, as the current version does not recognize the `riscv*` host tuples (there's no new version of ZeroMQ yet with newer ones).

  Good thing: RISC-V 64-bit toolchain packages can be installed out of the box on Ubuntu 18.04+.

  I would also like to add RISC-V 64-bit executables to gitian, but this will not be possible until #12511 .

Tree-SHA512: 358ed72ee9e4ae44e7d305c09a4ff5ce5460eeb7ed915eb25d39c8f43b61e7b347f51bf0ae5d83ddb4ce8876dea7703c926b3baa3cccb4932b3bc17160d801bb

depends/packages/openssl.mk

@@ -52,6 +52,8 @@ $(package)_config_opts_aarch64_linux=linux-generic64
 $(package)_config_opts_mipsel_linux=linux-generic32
 $(package)_config_opts_mips_linux=linux-generic32
 $(package)_config_opts_powerpc_linux=linux-generic32
+$(package)_config_opts_riscv32_linux=linux-generic32
+$(package)_config_opts_riscv64_linux=linux-generic64
 $(package)_config_opts_x86_64_darwin=darwin64-x86_64-cc
 $(package)_config_opts_x86_64_mingw32=mingw64
 $(package)_config_opts_i686_mingw32=mingw

depends/packages/zeromq.mk

@@ -13,7 +13,8 @@ endef
 
 define $(package)_preprocess_cmds
    patch -p1 < $($(package)_patch_dir)/0001-fix-build-with-older-mingw64.patch && \
-   patch -p1 < $($(package)_patch_dir)/0002-disable-pthread_set_name_np.patch
+   patch -p1 < $($(package)_patch_dir)/0002-disable-pthread_set_name_np.patch && \
+   cp -f $(BASEDIR)/config.guess $(BASEDIR)/config.sub config
 endef
 
 define $(package)_config_cmds